Three-way poppet valves are common in the existing art and are used in many applications for controlling and directing the flow of liquids or gases from either one of two discrete inlet ports to a single common outlet port. They are commonly constructed with an axially movable poppet located inside a valve body with a cylindrical bore. A biasing shaft is connected to the poppet to transmit a bias force to the poppet. Common methods for applying the bias force to the shaft include springs, pneumatic or hydraulic cylinders, and solenoid coils.
In some constructions, the discrete valve inlets and seats are located at each end of the cylindrical bore of the valve body with the common outlet located between the two inlets. The valve poppet, with valve members on both ends, is biased against one seat at one end of the cylindrical bore to stop flow from that inlet while at the same time the poppet bias pulls the poppet sealing member away from the seat at the opposite end of the cylindrical bore allowing flow to commence from the one open discrete inlet to the common outlet. Reversing the bias of the poppet closes the open inlet and opens the closed inlet, thus allowing flow from the formally closed discrete inlet to the common outlet.
Elastomeric seats are commonly used in three-way poppet valves as the material provides for an excellent and reliable dynamic seal at both low and high fluid pressures. Because elastomeric materials are resilient, such seals generally require a minimal force to create a seal at either low or high fluid pressure. Many designs employ o-rings constrained in a groove on the poppet that seal either laterally against a cylindrical bore or as a face seal against a flat surface.
A distinct disadvantage typical of poppet valves of the construction just described becomes evident during the axial movement of the poppet when both inlets and the outlet can be in fluidic communication. Because the direction of fluid flow will always be from the high pressure port to the low pressure port, unintentional and undesirable backflow can occur through the lowest pressure inlet until the poppet completes its axial movement and pressure at the common outlet drops below the pressure at the open inlet. The typical solution for preventing backflow is to use one or more external check valves in the inflow lines.
Further, while elastomeric valve seats are adequate for many applications, they have limitations. For example, elastomers typically are not very resistant to abrasion and thus are prone to damage from contaminants in the fluids and wear from repeated valve cycling. Elastomers can also suffer from degradation caused by chemical attack or extreme low or high temperatures. Thermoplastic materials have sometimes been used as a replacement for elastomers when such conditions apply. However, thermoplastic materials, unlike elastomeric materials, are typically not resilient and therefore are not well suited to provide for a reliable dynamic seal.